Cyclomorphosis of Bosmina (Eubosmina) tubicen, expressed as allometric growth of antennules and mucrones, was followed in 5 populations in the Okefenokee Swamp. Allometry of antennules was strongly cyclical, being positive in fall, winter and spring, but negative in early summer. Antennule allometry and other morphological variables (egg size, body size, antennule and mucro length) were all negatively correlated with temperature, but mucro allometry had a radically different pattern than the antennule-body size cyclomorphosis. Populations could be separated between lakes according to allometry of the mucrones, and mucro allometry was also negatively correlated with zooplankton population density. Morphological data from this study do not support serial replacement of morphotypes within lakes, and correlation with ecological parameters does not support the hypothesis that cyclomorphosis is caused by the presence of invertebrate predators.